Sorry to resurrect a dead thread, but if you're still looking for a solution then it might be worth you time looking on Aliexpress.
I found the 22-pin 0.5mm pitch ribbon cables that are required to connect to the RPI Zero camera connector.
If you make yourself a custom PCB and use this 22 pin connector (https://goo.gl/jvYe3p
) and place one on either side of the board.
Then buy yourself either a same side or reverse direction ribbon cable from the links below and that should sort out your extension problem.
Same Side: https://goo.gl/ap8kNg
Reverse Side: https://goo.gl/ejVjge
For your exact problem you wanted 40cm or 400mm for conversion purposes.
So here is a link to a 40cm cable: https://goo.gl/gA9ASM
If you want different sizes then you can go here: https://goo.gl/wUHYXc
However this is only for same sided cables as there are limited options for reverse side.